Today, the personnel ESD testing has become a mandatory requirement in ESD-Protected Areas (EPA). In many EPA areas, the testing and recording of ESD footwear and wrist-strap is manually conducted in “fuzzy” traditional ways. One most popular traditional way is to use a tester with a high resistance limit and a low resistance limit. When the wrist-strap or footwear under test has a resistance above the high limit, a high-fail LED will turn on. When the measured resistance is between the high and low limits, a pass LED will turn on. When the measured resistance is below the low limit, a low-fail LED will turn on. The measured result is fuzzy because it did not calculate and display the actual resistance being measured. Such “fuzzy” testing has created many issues in the fields that implemented an ESD-Control program. One of the major issues is the low accountability of the test results.
Conventionally, to test the normal functionality of a wrist strap or a footwear, simple traditional testing devices as described in the above paragraph are used. The traditional testing is to find out at testing time whether the device-under-test (DUT) is good or bad. If the ESD grounding device is found to be bad, then it will be discarded and replaced by a good one. In many applications, this replacement action turns out to be a bit too late since many of the ESD-sensitive (ESDS) products could have been damaged by the operators working on them wearing failed ESD grounding devices. Such situation is particularly critical in highly ESD sensitive areas such as aerospace electronics assembly plants or military-related production lines. A more desirable way of handling such cases is to identify the “About-To-Fail” (ATF) grounding devices and avoid using them when work in the EPA. Using such a well-managed scheme, we can effectively prevent the sudden failure of ESD grounding devices during work and essentially reduce the chances of ESD damages to the ESDS products during manufacturing or other sensitive operations.
In a traditional test, separate tests are usually applied to the footwear and the wrist strap. The test is inconvenient and time consuming, and many potential errors are generated, especially in the test of footwears. In testing the footwear, both feet of the user stand upon a single metal plate. If either one of the footwear passes the test, the test for footwear is then considered to pass the overall test. This is incorrect according to the international standards such as ANSI/ESD S20.20 or IEC-61340. This is because that it is impossible for a person to walk with both feet on the ground at the same time. In normal situation, one feet must be off the ground when a person walks. Once the footwear failing the test touches the ground, the person is not grounded transiently. During that short moment, the static electricity may be generated and harm the ESD-sensitive objects that a person may touch. All this is due to a defect in the footwear testing.
Using the traditional ways of wrist-strap and footwear testing, the test result is fuzzy and not precise so that the people under test can pass the test easily even some faulty results may occur in the test process. The test result is fuzzy because it is derived from resistance comparison with the high and low resistance limits without actual resistance calculation. The wrist strap and footwear are tested at separate times. Time is consumed and the operations are inconvenient.
Accordingly, the object of the present invention is to provide a method for testing personnel ESD grounding devices with a function of near-fail alert and a device for performing the same; in that a near-fail range is provided so that the user can receive an alert when the wrist straps or footwears worn on will fail soon in the near future and thus the user is reminded to take proper actions to change or fix the personnel ESD grounding device to prevent its sudden failure during actual use. Furthermore, the test provides digital readouts and has higher precision to avoid faulty results. Moreover, the wrist strap and footwear are tested simultaneously and individual results can be derived so as to avoid errors in test.
To achieve above object, the present invention provides a method for testing personnel ESD grounding devices with a function of near-fail alert; in that a near-fail range is set; when the measurement of the resistance of a wrist strap or a footwear is within the near-fail range; an alarm is actuated to alert the user that the static electricity prevention devices worn by the user will fail soon. The method further comprises the steps of: connecting the wrist-strap and/or footwear to be tested to the tester; pressing an actuating button to form a measuring voltage of each object to be tested; deriving a real voltage by operating the measured voltage with a reference voltage; deriving a value of resistance of the object to be tested by an operation to the real voltage; comparing the value of resistance with an upper limit and a lower limit for the object to be tested, wherein the upper limit and lower limit may be based on international standards such as ANSI/ESD S20.20; if the value of resistance is within a range between the upper limit and the lower limit, the object to be tested passes through the test and a pass indication to indicate the result is actuated; if the resistance value is out of a range between the upper limit and the lower limit, the object to be tested does not pass the test and a fail indication for indicating the result is actuated; and if the value of resistance has a difference from the upper limit or the lower limit within a predetermined range and is within the okay range between the upper limit and the lower limit; the value of resistance is at a range of near-fail, and a near-fail indication is actuated for alerting the user to replace the about-to-fail wrist-strap or footwear to prevent failure or to keep attention to such situation; and the predetermined range is settable as necessary by the user.
The present invention further provides a testing device for testing personnel ESD grounding wrist-strap or footwear with a function of near-fail alert. Basically the tester produces near-fail alarm in the following way: a near-fail range is set in the tester; when the measurement of the resistance for a wrist strap or a footwear is within the near-fail range; an alarm is actuated to alert the user that the static electricity prevention devices worn by the user will fail soon.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when it is read in conjunction with the appended drawings.